The present invention pertains to truck cranes, particularly those of the self-propelled mobile type and having a revolvable upper from which extends a telescoping boom. These prior art devices have various types of main frames and combinations of fore and aft and transverse outriggers for stabilizing the crane when in the boom operative position. Examples of such prior art devices are shown in the U.S. Pat. No. 3,854,595 issued Dec. 17, 1974 to Kuhn, which discloses a truck crane having a center portion from which transversely extending outriggers can swing and otherwise utilize a conventional undercarriage; U.S. Pat. No. 2,914,194 which issued Nov. 29, 1959 to Brown and which also utilizes a conventional undercarriage frame; and U.S. Pat. No. 4,160,558 of July 10, 1979 to Fritsch which utilizes mid-mounted, scissors type outriggers and a rectangular cross-section main frame.